Under-track device for use on railroads



Feb. 13, 1962 J. w. CHRISTOFF 3,020,853

UNDER-TRACK DEVICE FOR USE ON RAILROADS Filed July 3, 1958 5 Sheets-Sheet 1 Feb. 13, 1962 J. w. CHRISTOFF UNDER-TRACK DEVICE FOR USE ON RAILROADS 5 Sheets-Sheet 2 Filed July 3, 1958 n n "l i l ld." "H".

Feb. 13, 1962 J. w. CHRISTOFF UNDER-TRACK DEVICE FOR USE ON RAILROADS 5 Sheets-Sheet 3 Filed July 3, 1958 Jana lD-Ch-n': r qhpugpbm A 'rrnnuEYS OW @W w W vU Feb. 13, 1962 J. w. CHRISTOFF UNDER-TRACK DEVICE FOR USE ON RAILROADS 5 Sheets-Sheet 4 Filed July 3, 1958 Feb. 13, 1962 Filed July 5, 1958 J. W. CHRISTOFF UNDER-TRACK DEVICE FOR USE ON RAILROADS 5 Sheets-Sheet 5 3,020,853 UNDER-TRACK DEVICE FDR USE ON RAILRGADS James W. Christofi, Minneapolis, Minn, assignor to Mannix Qo. Ltd, Calgary, Alberta, Canada Filed July 3, 1953, Ser. No. 746,451 '7 Claims. (Cl. 104--7) This invention relates to an undertrack device which can be used either as a ballast sled or a ballast plow.

Ballast plows are employed for removing fouled ballast from a railroad roadbed. A ballast plow is inserted between the roadbed and the ties to which the track rails are secured and is then towed along the track in this position by a locomotive or other device, such as a winch car. As the plow progresses, it raises the ties from the roadbed ahead of it, supports the ties and the track secured thereto, as the device passes underneath, and finally allows the ties and track to settle back onto the roadbed or sub-grade behind the device. The weight of the ties and track supported by the plow is considerable and the plow is therefore pressed firmly down against the ballast. By providing the plow with one or more scraper blades, it is possible to separate a layer of ballast and displace this ballast to one or both sides of the track beyond the ends of the ties, this displaced ballast being readily removable when the ties resettle, since the lateral edges of the plow lie outwardly of the ends of the ties. Reference may be made to L. B. Franco and J. C. Stein U.S. Patent No. 2,921,390 issued January 19, 1960 for an example of a ballast plow.

Ballast sled devices are similar to ballast plows in that they are inserted between the roadbed and the ties and are towed along in this position. Sleds, however, are used either during the laying down of new tracks or to perform a reballasting operation following the pulling of a ballast plow in the manner just described. After the plow has removed a layer of fouled ballast, or in the case of a new track laid directly on the sub-grade, after the track has been so laid, fresh clean ballast is dumped onto the track to lie on top of the ties and rails. The function of the sled is to raise the ties up to their desired level and distribute the ballast evenly beneath them. Subsequently additional ballast will normally be dumped on the track between each pair of adjacent ties, this latter operation usually being carried out manually, since it does not require raising of the track. Reference may be made to L. B. Franco U.S. Patent No. 2,769,172 issued October 30, 1956, for an example of a ballast sled.

There is much in common between the basic structure of a ballast plow and a ballast sled, the fundamental difference being that the plow uses scraper blades for deflecting ballast, whereas the sled uses levelling blades for smoothing out ballast. In other respects, the two devices function in a very similar manner, each being required to move along the roadbed while lifting and supporting a span of track. Both devices consist of a generally flat framework of rigid construction, this framework including essentially a plate of metal, upper runner means for slidingly and supportingly engaging the ties and either scraper blades (in the case of the plow) or under-runners and levelling blades (in the case of the sled).

The scraper blades of a plow are distinguished from the levelling blades of a sled in that the scraper blades are inclined forwardly and downwardly so as to dig into the ballast encountered by the plow, thus disturbing such ballast and causing the same to travel upwardly along the surface of the scraper blade, Additionally, the scraper blades extend to one or both sides of the plow States atent ice in a rearward direction, so that ballast that has been disengaged from the roadbed and is lying free in front of the blade will be caused to travel rearwardly and outwardly along the face of the blade ultimately to be projected beyond the lateral edges of the plow for subsequent collection.

In contrast, the levelling blades of a sled are inclined downwardly and somewhat backwardly in relation to the direction of travel of the sled so that they do not dig into the ballast encountered but press downwardly on such ballast with their trailing edges to perform a levelling function.

Hitherto, by reason of this difference in the blade structure, it has been customary to construct ballast plows and ballast sleds as entirely separate devices.

The object of the present invention is to provide a combined device which can function either as.a plow or a sled, as required, provision being made for movement of the same set of blades between plowing and sledding positions.

The various features of the invention will become apparent from consideration of the under-track device illustrated by way of example in the accompanying drawings, and from the appended claims.

In the drawings:

FIGURE 1 shows a top plan view of the device with the blades in their raised inoperative position;

FIGURE 2 shows a side view of the device seen in FIGURE 1;

FIGURE 3 shows an underside plan view of the device seen in FIGURES 1 and 2;

FIGURE 4 is a section on the line IVIV in FIG- URE 1;

FIGURE 5 is a fragmentary sectional view through a blade showing the connection of such blade to hydraulic operating means, this view being taken on the line V-V in FIGURE 1;

FIGURE 6 is a view similar to FIGURE 5 but showing the parts in a first operating position, the sledding position;

FIGURE 7 is a further view of the same parts in a second operating position, the plowing position;

FIGURE 8 is a fragmentary sectional view taken on the line VIIIVIII in FIGURE 1;

FIGURE 9 is a section taken on the line IXIX in FIGURE 8;

FIGURE 10 is a view similar to FIGURE 9 showing the parts in a different position;

FIGURE 11 is a diagrammatic plan view of the device in operation on a length of track, when used as a plow;

FIGURE 12 is a side View of FIGURE 11;

FIGURE 13 is a view generally similar to FIGURE 12 but showing the device in use as a sled;

FIGURE 14 is an enlarged view of the device in use as a sled, the parts being shown in section taken on the line XIVXIV in FIGURE 1; and

FIGURE 15 is a diagrammatic view showing the hydraulic circuit for operating the blade actuating means.

The device 10 consists of a framework structure of welded construction comprising a main plate 11 of rigid steel, to the underside of which there is secured a centrally located spine in the form of a downwardly projecting bar 12 extending from front'to rear along the centre line of the plate 11. This bar 12 and a number of downwardly projecting posts 13 serve to secure to the plate 11 five under-runners 14, 15, 16, 17 and 18. The outer under-runners 14 and 18 are slightly tapered and upwardly curved at their leading edges, and these runners together with the central under-runner 16, terminate at the leading edge 19 of the plate 11. The intermediate under-runners 15 and 17 continue beyond the Patented Feb. 13, 1962 leading edge 19 of the plate 11 while constituting the lower flanges of a pair of I-beams 20 and 21 and forming the leading lower sliding surfaces of the device. The webs of these I-beams terminate at points 22 and 23 respectively just rearwardly of the leading edge 19 of the plate 11. The upper flanges 24 of the I-beams 20 and 21 are inclined downwardly and forwardly to meet the under-runners 15 and 17, pointed tips 37 and 38 being secured to the under-runners 17 and 15 respectively to extend beyond the forward edges of forward portions 25 and 26 of upper runners 27 and 28, such forward ends 25 and 26 being supported by the upper I-beam flanges. The upper runners 27 and 28 extend rearwardly from their forward portions 25 and 26 along the upper side of the device to form the surface along which the ties slide during pulling of the device under a section of track.

The forward ends of the outer under-runners 14 and 18 are provided with short I-beams 29 and 30, the lower flanges of which are constituted by the forward ends, the under-runners 14 and 18 and the upper flanges 31 and 32 of which underlie the forward lateral edges of the plate 1].. Towing ears 33 and 34 are provided on the upper surfaces of the forward lateral edges of the plate 11, these ears being provided with holes 35 and 36 respectively to receive shackles on the end of towing cables, as appears from FIGURE 11 which will subsequently be described.

The device is provided with four metal blade-supportin g moleboards 40, 41, 42 and 43. The leading moleboards 40 and 42 are secured by hinges 44 and 45 respectively to the leading edges of elongated cavities 46 and 47 cut in the plate 11, these hinges extending rearwardly and outwardly towards the lateral edges of the device from a position adjacent the forward end of the central spine 12. The other pair of moleboards 41 and 43 are secured by hinges 48 and 49 respectively to the rearmost edges of the plate 11, such rear edges being cut in the shape of a V having its apex disposed forwardly and at the centre of the device. Each of the moleboards 40, 41, 42 and 43 carries a blade 50, 51, 52 and 53 respectively, and each is controlled by a hydraulically operated cylinder 55, 56, 57 and 58 respectively, each such cylinder having a respective piston 59, 60, 61 and 62.

FIGURES to 7 show on an enlarged scale a typical such moleboard and blade assembly 41 and 51, the other assemblies being similar. It will be seen from these figures that the blade 51 is secured to the moleboard 41 by nut and bolt assemblies 54. The piston 60 is pivotally secured to the moleboard 41 by means of a bracket 63, the remote end of the cylinder 56 being pivotally mounted by means of a bracket 64 on a transverse supporting member 67 which extends across the rear of the device from the ends of the upper runners 27 and 28 to the undersurfaces of which it is secured. As appears from FIG- URE l the two forward cylinders 55 and 57 are secured to the body of the plate 11 rearwardly of the two cavities 46 and 47 therein, while the more rearward cylinders 56 and 58 are mounted on the members 67.

For simplicity, no hydraulic connections have been shown in the views described so far, the entire hydraulic circuit being illustrated separately in FIGURE 15. It will be evident, however, that admission of hydraulic fluid to the remote end of the cylinder 56 through port 65 will cause the piston 60 to be moved outwardly of the cylinder 56 to bring the parts to the position shown in FIGURE 6 to place the moleboard 41 and the blade 51 in the sledding position. The introduction of further hydraulic fluid through the port 65 will move the piston 60 to its fully extended position shown in FIGURE 7 which will bring the moleboard and blade assembly to a plowing position. When it is desired to return the blade assembly to either the sledding position of FIGURE 6 or the fully retracted position of FIGURE 5, hydraulic fluid can be introduced through the other port 66.

On a platform 70 secured to one upper side edge of the plate 11 there are mounted four master hydraulic cylinders 71, each such cylinder being controlled by a respective manually operable handle 72. The two more rearward master cylinders 71 control the flow of hydraulic fluid along pipes 75 and 76 (see FIGURE 15). A pipe 75 leads to the rear end of each of the rearward pair of operating cylinders 56 and 58 from a respective master cylinder 71, and a pipe 76 leads to the forward end of each of these same operating cylinders. Similar pipes 77 and 78 lead from each of the forward master cylinders 71 conveying fluid to the respective ends of each of the two forward operating cylinders 55 and 57 that control the blades 50 and 52.

Forwardly of the central bar 12 there is provided, as shown by FIGURES 8 to 10, a continuation of said bar in the form of a gate 89 which is pivotally secured to the plate 11 at the top and the under-runner 16 at the bottom by means of a vertically extending pin 81 that extends through a cylindrical boss 82 formed at the rear end of the gate 80. The gate is thus swingable between 21 directly forwardly projecting position as it is shown in FIGURES 8 and 9, and one or more deflected positions. The position occupied by the gate 80 when deflected fully to the left is shown in FIGURE 10. Once a required position of the gate 80 has been determined, it can be held in that position by means of a further pin 83 which passes down through the plate 11 and a boss 84 at the leading end of the gate 80. In passing through the plate 11 this pin 83 employs one or other of a series of holes 85 formed in the plate 11 in an are around the pivot pin 81. When the device is used as a sled, the gate 80 is always placed in the fully forward position. It may be moved to one or other of its sideways positions such as the extreme lefthand position shown in FIGURE 10, when the device is to be used as a plow. It then acts as a forward continuation of the blade 50.

The manner of operation of the device when used as a plow is illustrated in FIGURES 11 and 12. The device is placed under the track and all the blades are moved to the FIGURE 7 position. The device is then towed by means of cables from a towing bar 91 connected by further cables 92 to a mounting 93 which is slidable on a transverse bar 94 secured to the rear of a flat car 95. Control over the transverse movement of the mounting 93 along the bar 94 is effected by means of a screwthreaded rod 96 controlled by a handle 97. The purpose of this transversely slidable mounting is to be able to move the towing bar 91 to one side or other of the track to compensate for curvature of the track to avoid the plow 10 tending to cut the corner on a curve.

This assembly is towed along the track by means of a locomotive 98. As appears most readily from FIGURE 12, the plow is being employed to skeletonize or plow out the track. Initially, in front of the plow 10, the ties 99 are resting on a layer of ballast 199 which in turn rests on the sub-grade 101. The advancing plow 10 slides over the sub-grade 101, raises the track in advance of the plow, and plows the ballast 100 out of the two sides of the track (as best appreciated from FIGURE 11). Rearwardly of the plow, the track settles back onto the subgrade 101.

In order to function in this manner as a plow it is necessary for the blades to have a substantial sweep-back angle, that is the angle which each blade hinge (44, 45, 48', 49) makes with the transverse direction of the device. In the device illustrated, the sweep-back angle of each blade is 45. This may be reduced somewhat, but at the expense of efiiciency. With a blade angle below approximately 30, the device will not plow at all, but when pulled with the blades in the plowing position merely lifts vertically upwards and travels along the top of the ballast, no defiection of the ballast to the sides taking place. A sweepback angle of approximately 30 may thus be taken as the minimum, although a greater angle, of the order of 45, is preferred. The angle may be increased indefinitely as 5. far as effective plowing is concerned, but above .about 45 it renders the device unnecessarily lengthy and thus begins to introduce other undesirable factors.

The function of the gate 80 is to compensate for track irregularities. It is not uncommon for trafiic on the track to produce regions in which there is more ballast at one end of the ties than at the other after the ballast has been in position for some years. In this case, the forward end of the gate will be positioned to that side of the track on which there is more ballast, so that some ballast from that side is carried across to the other side of the track, with the result that approximately the same amount of ballast is ultimately deflected beyond each side of the track.

In the embodiment described, the gate has been shown as pivotally mounted, as this is convenient, but clearly a completely detachable plate could be employed. A detachable plate would be particularly suitable if a large quantity of ballast were required to be deflected across the plow from one side to the other, requiring the plate to be rather longer than is shown in the accompanying drawings.

If the plow is taking a deep cut, then the front gate will nearly always be in the forward position. It is only practical to place the gate in one of its side positions when a comparatively shallow cut is being taken.

The ability to make fine adjustments to the blade positions is of considerable practical value when the device is being used as a plow. When proceeding 'down the track, a section of track requiring a different cutting angle to the blades is sometimes encountered. At one point the ballast may be very muddy, usually in parts where drainage is bad, and then in the next section of track, the ballast may be firm and in very different condition. These two different conditions require different cutting angles for best plowing effect.

When the device is used as a sled, the blades are adjusted in the sledding position shown in FIGURE 6. FIGURE 13 is a view of a similar nature to FIGURE 12 showing the operation when ballasting, i.e. when used as a sled. The track in advance of the device is now assumed to have been plowed free of ballast so that the ties 99 are resting directly on the sub-grade 101. Fresh ballast 102 has been dumped on the track from a fiat car to rest between and on top of the ties. As the sled 10 advances, being pulled along by towing cables 90 and a similar towing assembly to that already described in FIGURES 11 and 12, it raises the track in advance of itself allowing the ballast 102 to remain on the sub-grade in discrete piles. The function of a ballast sled has been fully described in the prior patent referred to above and also in James W. Christoifs US. patent application Serial No. 647,523 filed March 21, 1957, the piles of ballast 102 being smoothed out by the blades into a comparatively smooth layer of ballast 103 in rear of the sled. The ties 99 settle onto this layer 103 behind the sled and subsequently further fresh ballast will be dumped manually between these ties. A ballast sled may also be employed simply for lifting a section of track onto its own old ballast without a prior plowing operation. The gate 80 will always be in the forward position when the device is being used as a sled.

An aspect of the ballasting operation is illustrated in a fragmentary enlarged view shown in FIGURE 14 which shows a central ballast levelling flap 86 pivotally mounted by hinge 87 to the underside of the plate 11 at the rear edge of the bar 12, this flap 86 co-operating with the end of the blade 51 and its associated moleboard 41, in the manner fully described in the application just referred to. When the device is used for plowing, the flap 86 takes up the position shown in broken lines in FIGURE 14. In this position it extends somewhat below the bottom level of the blades 51 and 53 and thus tends to form a shallow channel in the subgrade along the centre of the track. This is no disadvantage in practice, in fact it may be. desirable, as tending to minimise any tendency for a centre-bound track to be formed ultimately. A centre-bound track is one in which the level of ballast along the centre is higher than at the edges, thus tending to stress the ties in bending about the central hump of ballast. A centre-bound track is thus to be carefully avoided, even at the risk of some deviation in the opposite direction from a perfectly fiat ballast bed.

An important advantage of the present invention is the rapidity with which the device can be changed from a plow to a sled and vice versa, without the need for removing the device from beneath the track. Experience has shown that when a ballast sled is being used for raising the track onto old ballast, it is sometimes found that a section of track is reached which is particularly bad and which should, in accordance with good railroad practice, be removed. With a simple ballast sled this is an impossibility without first removing the sled from the track and replacing it with a plow. The insertion and removal of these devices is the most time consuming aspect of the whole job and it is desirable to keep the number of these operations to a minimum. A device according to the present invention can quickly be changed over to take on the'function of a plow for the short section of bad track, and just as quickly reconverted into a sled when the bad section of track has been passed.

This application is a continuation-in-part of application Serial No. 669,772 filed July 3, 1957 (now abandoned).

- I claim:

1. An under-track device for handling ballast under railroad tracks and ties, said device comprising a generally flat framework constructed to be drawn along between the roadbed and the ties while supporting the weight of said ties and a span of track, said framework comprising under-runner means secured to the underside of the framework to space said framework above the bottom of the device so that a substantial portion of the ballast passes under said plate, a pair of spaced apart, parallel, upper runners mounted on the upper side of said framework to extend upwardly therefrom for engagement with the undersurfaces of the ties, at least one elongated blade extending at an inclination to the transverse direction of the device, means pivotally mounting said blade on said framework to be movable between a plowing position in which it projects downwardly and for- Wardly of said framework and a ballast levelling position in which it extends downwardly and rearwardly of said framework, and control means for moving said blade between said positions and for retaining said blade, as desired, at either of said positions and at any other posi-. tion intermediate therebetween, the sweep-back angle of each-said blade being'of sufficient magnitude for said blade when in said plowing position to deflect ballast to aside of the device. I

'2. An under-trackdevice for handling ballast under railroad tracks and ties, said device comprising a generally flat framework constructed to be drawn along between the roadbed and the ties while supporting the weight 'of said ties and a'span of track, said framework comprising a plate, under-runner means secured to the underside of the plate to space said plate above the bottom of the device so that a substantial portion of the ballast passes undersaid plate, a pair of spaced apart, parallel, upper runners mounted on the upper side of said plate to extend upwardly therefrom from engagement with the undersurfaces of the ties, a pair of elongated blades respectively extending outwardly and rearwardly to opposite lateral edges of said plate from a position adjacent the longitudinal centre line of said plate, means pivotally mounting each of said blades on said plate so as to be movable between a plowing position in which said blade projects downwardly and forwardly of said plate and a ballast levelling position in which said blade extends downwardly and rearwardly of said plate, and control means for moving each of said blades between said positions and for retaining each of said blades, as desired, at either of said positions and at any other position intermediate therebetween, the sweep-back angle of each said blade being of sufficient magnitude for said blade when in said plowing position to deflect ballast to a side of the device.

3. An under-track device as claimed in claim 2, wherein said control means comprises a fluid-pressure-operated, double-acting, cylinder and piston assembly, and manually operable means connected for directing pressure fluid to either end of said assembly.

4. An under-track device for handling ballast under railroad tracks and ties, said device comprising a generally flat framework constructed to be drawn along between the roadbed and the ties while supporting the weight of said ties and a span of track, said framework comprising a plate, under-runner means secured to the underside of the plate to space said plate above the bottom of the device so that a substantial portion of the ballast passes under said plate, a pair of spaced apart, parallel, upper runners mounted on the upper side of said plate to extend upwardly therefrom for engagement with the undersurfaces of the ties, two pairs of elongated blades, each pair of blades respectively extending outwardly and rearwardly to opposite lateral edges of said plate from a position adjacent the longitudinal centre line of said plate, one such pair being disposed rearwardly of and in alignment with the other said pair, means pivotally mounting each of said blades on said plate to be movable between a plowing position in which it projects downwardly and forwardly of said plate and a ballast levelling position in which it extends downwardly and rearwardly of said plate, and control means for moving each of the blades between said positions and for retaining each of said blades, as desired, at either of said positions and at any other position intermediate therebetween, each said blade being swept back at an angle to the transverse direction of the sled not less than approximately 30 whereby when in said plowing position to deflect ballast to a side of the device.

5. An under-track device for handling ballast under railroad tracks and ties, said device comprising a generally flat framework constructed to be drawn along between the roadbed and the ties while supporting the weight of said ties and a span of track, said framework comprising a plate, under-runner means secured to the underside of the plate to space the plate above the bottom of the device so that a substantial portion of the ballast passes under said plate, a pair of spaced apart, parallel, upper runners mounted on the upper side of said plate to extend upwardly therefrom for engagement with the undersurfaces of the ties, two pairs of elongated blades, each pair of blades respectively extending outwardly and rearwardly to opposite lateral edges of said plate from a position adjacent the longitudinal centre line of said plate, one such pair being disposed rearwardly of and in alignment with the other said pair, means pivotally mounting each of said blades on said plate to be movable between a plowing position in which it projects downwardly and forwardly of said plate and a ballast levelling position in which it extends downwardly and rearwardly of said plate, each said blade being swept back at an angle to the transverse direction of the sled not less than approximately 30 whereby when in said plowing position to deflect ballast to a side of the device, a fiuid-pressure-operated, double-acting, cylinder and piston assembly associated with each of said blades and extending between a part of each such blade and said plate, and four separate manually operable means each connected for directing fluid pressure selectively to the respective ends of a said cylinder associated with a respective blade for retaining said respective blade, as desired, at either of said positions and at any other position intermediate therebetween.

6. An under-track device for handling ballast under railroad tracks and ties, said devices comprising a generally flat framework constructed to be drawn along between the roadbed and the ties while supporting the weight of said ties and a span of track, said framework comprising a plate, under-runner means secured to the underside of the plate to space the plate above the bottom of the device so that a substantial portion of the ballast passes under said plate, a pair of spaced apart, parallel, upper runners mounted on the upper side of said plate to extend upwardly therefrom for engagement with the undersurfaces of the ties, two pairs of elongated blades, each pair of blades respectively extending outwardly and rearwardly to opposite lateral edges of said plate from a position adjacent the longitudinal centre line of said plate, one such pair being disposed rearwardly of and in alignment with the other said pair, means pivotally mounting each of said blades on said plate to be movable between a plowing position in which it projects downwardly and forwardly of said plate, a ballast levelling position in which it extends downwardly and rearwardly of said plate, and a retracted position in which it lies substantially in the plane of the plate, and control means for moving each of the blades between said positions and for retaining each of said blades, as desired, at either of said positions and at any other position intermediate therebetween, each said blade being swept back at an angle to the transverse direction of the sled not less than approximately 30 whereby when in said plowing position to deflect ballast to a side of the device.

7. An under-track device for handling ballast under railroad tracks and ties, said device comprising a generally flat framework constructed to be drawn along between the roadbed and the ties while supporting the weight of said ties and a span of track, said framework comprising a plate, under-runner means secured to the underside of the plate to space the plate above the bottom of the device so that a substantial portion of the ballast passes under said plate, a pair of spaced apart, parallel upper runners mounted on the upper side of said plate to extend upwardly therefrom for engagement with the undersurfaces of the ties, a pair of elongated blades respectively extending outwardly and rearwardly to opposite lateral edges of said plate from a position adjacent the longitudinal centre line of said plate, said blades occupying a plowing position in which they project downwardly and forwardly of said plate, the sweep-back angle of each said blade being of sutficient magnitude for said blade when in said plowing position to deflect ballast to a side of the device, further blade member movably mounted on said framework to be movable between a first position in which it extends directly forwardly from the apex formed by the mutually adjacent leading ends of said blades and a second position in which said blade member forms a forwardly and sidewardly projecting extension of one of said blades, and means for securing said blade member in either such position.

References Cited in the file of this patent UNITED STATES PATENTS 1,487,723 Corbitt Mar. 25, 1924 2,062,544 Weeks Dec. 1, 1936 2,769,172 Franco Oct. 30, 1956 FOREIGN PATENTS 518,999 Canada Nov. 29, 1955 142,755 Sweden Nov. 3, 1953 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,020,853 February 13, 1962 James W, Christoff It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

l Column 6, line 40, for-"plate" read framework Signed and sealed this 12th day of June 1962'.

( SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents 

